diff --git a/lib/Basic/Diagnostic.cpp b/lib/Basic/Diagnostic.cpp
index 83ccd22..893eae5 100644
--- a/lib/Basic/Diagnostic.cpp
+++ b/lib/Basic/Diagnostic.cpp
@@ -175,7 +175,8 @@
 static void DummyArgToStringFn(Diagnostic::ArgumentKind AK, intptr_t QT,
                                const char *Modifier, unsigned ML,
                                const char *Argument, unsigned ArgLen,
-                               llvm::SmallVectorImpl<char> &Output) {
+                               llvm::SmallVectorImpl<char> &Output,
+                               void *Cookie) {
   const char *Str = "<can't format argument>";
   Output.append(Str, Str+strlen(Str));
 }
@@ -199,6 +200,7 @@
   LastDiagLevel = Fatal;
   
   ArgToStringFn = DummyArgToStringFn;
+  ArgToStringCookie = 0;
 }
 
 Diagnostic::~Diagnostic() {